VRM

Short for voltage regulator module, a small module that installs on a motherboard to regulate the voltage fed to the microprocessor. Nearly all motherboards have either a built-in voltage regulator or a VRM, the only difference being that the VRM is replaceable.

A voltage regulator module or VRM, sometimes called PPM (power processing module) is an electronic device that provides a microprocessor the appropriate supply voltage. It can be soldered to the motherboard or be an installable device. It allows processors with different supply voltage to be mounted on the same motherboard.

Some voltage regulators provide a fixed supply voltage to the processor, but most of them sense the required supply voltage from the processor. In particular, VRMs that are soldered to the motherboard are supposed to do the sensing, according to the Intel specification.

The correct supply voltage is communicated by the microprocessor to the VRM at startup via a number of bits called VID (voltage identificator). In particular, the VRM initially provides a standard supply voltage to the VID logic, which is the part of the processor whose only aim is to then send the VID to the VRM. When the VRM has received the VID identifying the required supply voltage, it starts acting as a voltage regulator, providing the required constant voltage supply to the processor.

VRMs are buck converters that convert from +5 V to a much smaller voltage required by the CPU -- some CPUs require 3.3 V, others require 1.10 V. Historically, CPU designers keep designing to smaller voltages; lower voltages help reduce CPU power dissipation.